The disclosures herein relate in general to electronic circuitry, and in particular to a method and circuitry for multi-stage amplification.
FIG. 1 (prior art) is a schematic electrical circuit diagram of a conventional multi-stage amplifier, indicated generally at 100. The amplifier 100 includes at least first and second stages 102 and 104, which are transconductance amplifiers whose gains are Gm1 and Gm2, respectively. The amplifier 100 receives a differential input voltage from lines S00 and S01.
The first stage 102 applies the gain Gm1 to amplify a difference (“ΔNIN”) between S00's voltage (“VIN+”) and S01's voltage (“VIN−”). Similarly, the second stage 104 applies the gain Gm2 to amplify a difference (“ΔV1”) between a line S10's voltage (“V10”) and a line S11's voltage (“V11”). Accordingly: (a) in response to ΔVIN, the first stage 102 generates a difference (“ΔI1”) between S01's current (“I10”) and S11's current (“I11”); and (b) in response to ΔV1, the second stage 104 generates a difference (“ΔI2”) between a line S20's current (“I20”) and a line S21's current (“I21”).
As shown in FIG. 1, S10 is connected to a resistor R10, which is coupled through a first terminal of an inductor L1 to a voltage supply node VDD. Also, S11 is connected to a resistor R11, which is coupled through a second terminal of L1 to VDD. Similarly, S20 is connected to a resistor R20, which is coupled through a first terminal of an inductor L2 to VDD. Further, S21 is connected to a resistor R21, which is coupled through a second terminal of L2 to VDD.
FIG. 2 (prior art) is a graph of an example curve 202 of gain (dB) versus frequency for the amplifier 100, having a 3 dB bandwidth region 204. As shown in FIG. 2, the 3 dB bandwidth region 204 is a range of frequencies whose gains are within 3 dB of peak gain. Without L1, L2, R10, R11, R20 and R21, performance the amplifier 100 could diminish, according to an example curve 206 having a 3 dB bandwidth region 208.
By comparison, with L1, L2, R10, R11, R20 and R21: (a) in the region 208, a dominant contribution to the 3 dB bandwidth region 204 is provided by R10, R11, R20 and R21; and (b) in a bandwidth expansion region 210, a significant contribution to the 3 dB bandwidth region 204 is provided by L1 and L2, in addition to contribution by R10, R11, R20 and R21.
Nevertheless, the amplifier 100 has shortcomings. For example, the amplifier 100 has one passive magnetic component (e.g., inductor) per stage. As a precaution against possible interference through magnetic field coupling (e.g., between coil windings of nearby inductors), a spacing is imposed between those passive magnetic components, which increases silicon area in an integrated circuit that contains the amplifier 100.